1. Field of the Invention
The present invention relates to a phase shift circuit for shifting the phase of a rectangular input signal by a predetermined time prior to output, and an FM detector circuit using the phase shift circuit.
2. Description of the Related Art
Heretofore, a quadrature detector circuit has been used for the FM detector circuit. The quadrature detector circuit shapes a delay signal by shifting the phase of an IF (intermediate frequency) signal by a predetermined time (substantially 90xc2x0 with respect to the center frequency), and performs FM detection by multiplying this delay signal with the IF signal. Therefore, the phase shift circuit becomes necessary for producing the delay signal.
The phase shift circuit comprises an ordinary phase shift circuit using coils and capacitors, a ceramic resonator, or the like.
However, in such a conventional phase shift circuit, the problems are that the coil and the ceramic resonator are external parts, circuit integration is difficult, and the circuit tends to become large.
Furthermore, although it is possible to use a delay line or the like, the problems are that the circuit becomes large, the temperature dependence increases, and so forth.
Taking into consideration the above-mentioned problems, it is an object of the present invention to provide a phase shift circuit having a simple configuration and performing phase shifts with stable delay times, and a detector circuit using this phase shift circuit.
In the present invention, a voltage rising at a predetermined slope is obtained by charging a capacitor with current from a constant current source. Thus, by setting a desired time (predetermined time) for delaying the point where the voltage exceeds a reference voltage, a pulse signal having a phase delayed by the predetermined time is obtained. On the other hand, a pulse signal having a phase delayed by the predetermined time can also be obtained in a similar manner for the inverted input signal. Thus, signals having their phases delayed by the predetermined time from the input signal from the rise of these two signals can be obtained.
In this manner, according to the present invention, signals having their phases delayed by predetermined times can be obtained from a simple circuit without the need for coils. Furthermore, resonators, delay lines, or the like are also unnecessary.